No abstract

Microorganisms play a vital role in shaping the soil environment and enhancing plant growth by interacting with plant root systems. Because of the vast diversity of cell types involved, combined with dynamic and spatial heterogeneity, identifying the causal contribution of a defined factor, such as a microbial exopolysaccharide (EPS), remains elusive. Synthetic approaches that enable orthogonal control of microbial pathways are a promising means to dissect such complexity. Here we report the implementation of a synthetic, light-activated, transcriptional control platform using the blue-light responsive DNA binding protein EL222 in the nitrogen fixing soil bacterium Sinorhizobium meliloti. By fine-tuning the system, we successfully achieved optical control of an EPS production pathway without significant basal expression under noninducing (dark) conditions. Optical control of EPS recapitulated important behaviors such as a mucoid plate phenotype and formation of structured biofilms, enabling spatial control of biofilm structures in S. meliloti. The successful implementation of optically controlled gene expression in S. meliloti enables systematic investigation of how genotype and microenvironmental factors together shape phenotype in situ.

AbstractMicroorganisms play a vital role in shaping the soil environment and enhancing plant growth by interacting with plant root systems. Due to the vast diversity of cell types involved, combined with dynamic and spatial heterogeneity, identifying the causal contribution of a defined factor, such as a microbial exopolysaccharide (EPS), remains elusive. Synthetic approaches that enable orthogonal control of microbial pathways are a promising means to dissect such complexity. Here we report the implementation of a synthetic, light-activated, transcriptional control platform in the nitrogen fixing soil bacterium Sinorhizobium meliloti. By fine tuning the system, we successfully achieved optical control of an EPS production pathway without significant basal expression under non-inducing (dark) conditions. Optical control of EPS recapitulated important behaviors such as a mucoid plate phenotype and formation of structured biofilms, enabling spatial control of biofilm structures in S. meliloti. The successful implementation of optically controlled gene expression in S. meliloti enables systematic investigation of how genotype and microenvironmental factors together shape phenotype in situ.SignificanceMicroorganisms are key players in sustaining the soil environment and plant growth. Symbiotic associations of soil microbes and plants provide a major source of nitrogen in agricultural systems, prevent water contamination from synthetic fertilizer application, and support crop growth in marginal soils. However, measuring the impact of microbial gene products on beneficial function remains a major challenge. This work provides a critical step toward addressing this challenge by implementing external gene regulation in a well characterized nitrogen fixing soil bacterium. We show that light exposure enables spatial and temporal control of the extracellular polysaccharide production functionality essential for symbiosis. Remote control of genes enables the benefits of candidate microorganisms to be systematically measured and enhanced within complex natural settings.

Soil protists are an important part of the microbial community in the rhizosphere. Plants grown with protists fare better than plants grown without protists.

Dysgonomonas spp. are facultative heterotrophs which colonize diverse environments, including the hindgut of the lower termite Reticulitermes flavipes. Dysgonomonas genomes are enriched for genes involving oligo- and polysaccharide utilization, enabling modification of a wide array of complex glycans. Here, we report draft genome sequences for Dysgonomonas sp. strains BGC7 and HGC4.